Method of controlling a rotary electrical machine, a servo-control system for implementing the method, and a rotary machine fitted with such a system

Abstract

A method of controlling the torque of a rotary machine powered by means of an inverter and servo-controlled by a system having sensors, an observer, and a computer which delivers controls to the switches of the inverter on the basis of values supplied to the observer by the sensors, in the form of sequences of three vectors to bring the torque Γ and the stator flux Φ S of the machine towards reference values for Γ ref and Φ Sref . The measurement sampling period is selected to be equal to the sequence period DTML which corresponds to half the switching period of the inverter. The characteristics of the vectors for each sequence are obtained by solving the following system of equations:  (  Γ  t a  t a +  Γ  t p  t p = Γ ref - Γ n t a + t p = DTML in which dΓ/dt a and dΓ/dt p are variations over time in torque respectively when an active vector V a or a passive vector V p is applied, Γ n being the present torque, and t a and t p are the respective times during which the vectors are applied.

What is claimed is:  
     
       1. A method of controlling the electromagnetic torque of a rotary machine having n phases powered via an inverter having n switches each having m states, thereby defining m n  states for a stator voltage vector V i , where i ε{1, . . . , m n }, the machine being servo-controlled in terms of electromagnetic torque Γ and stator flux Φ S  to a reference electromagnetic torque Γ ref  and a reference stator flux Φ Sref  by means of a servo-control system comprising a set of sensors, an observer, and a computer, the computer delivering control signals to the multi-state switches of the inverter in successive sequences of three successive commands, on the basis of values supplied to the observer by the sensors, the computer determining for each sequence, amongst the V i  possible states of the stator voltage vector, the three command vectors to be used in succession so as to bring the torque Γ and the stator flux Φ S  optimally towards the reference torque Γ ref  and the reference flux Φ Sref  and to command the multi-state switches accordingly, wherein, in a system where the sampling period for measuring purposes is selected to be equal to a period DTML specific to the sequences of three successive commands, which period is itself equal to half the switching period of the inverter, the instants and the durations for which the vectors of each sequence are obtained by solving the following system of equations:             (                      Γ            t   a              t   a       +            Γ            t   p              t   p         =       Γ   ref     -     Γ   n                       t   a     +     t   p       =   DTML                             
       in which: dΓ/dt a  corresponds to variation in time of the torque while an active vector V a  is being applied; dΓ/dt p  corresponds to variation in time of the torque while a passive vector V p  is being applied; Γ ref  is the reference torque; Γ n  is the present torque, and t a  and t p  are the times during which the active and passive vectors are respectively applied.  
     
     
       2. A method according to claim  1 , in which the time during which the active vector is applied for a sequence is shared on either side of the time during which the passive vector is applied, in accordance with the following equation:          t   1     =           2        (       Γ   ref     -     Γ   n       )        DTML     -       t   a   2          (     d                   Γ   /     dt   a         )       -         t   p          (     d                   Γ   /     dt   p         )          DTML           2        (     d                   Γ   /     dt   a         )       -       (     d                   Γ   /     dt   p         )          t   p           .                     
     
     
       3. A servo-control system for a rotary machine having n phases which is powered by an inverter having n switches each having m states, thereby defining m n  states for a stator voltage vector V i , where i ε{1, . . . , m n }, the machine being servo-controlled in terms of electromagnetic torque Γ and stator flux Φ S  to a reference electromagnetic torque Γ ref  and a reference stator flux Φ Sref  by means of a servo-control system comprising a set of sensors, an observer, and a computer, the computer delivering control signals to the multi-state switches of the inverter in successive sequences of three successive commands, on the basis of values supplied to the observer by the sensors, the computer determining for each sequence, amongst the V i  possible states of the stator voltage vector, the three command vectors to be used in succession so as to bring the torque Γ and the stator flux Φ S  optimally towards the reference torque Γ ref  and the reference flux Φ Sref  and to command the multi-state switches accordingly, the system implementing the method according to claim  1 . 
     
     
       4. An n-phase rotary machine powered via an inverter having n switches each having m states, thereby defining m n  states for a stator voltage vector V i , where i ε{1, . . . , m n }, the machine being servo-controlled in terms of electromagnetic torque Γ and stator flux Φ S  to a reference electromagnetic torque Γ ref  and a reference stator flux Φ Sref  by means of a servo-control system comprising a set of sensors, an observer, and a computer, the computer delivering control signals to the multi-state switches of the inverter in successive sequences of three successive commands, on the basis of values supplied to the observer by the sensors, the computer determining for each sequence, amongst the V i  possible states of the stator voltage vector, the three command vectors to be used in succession so as to bring the torque Γ and the stator flux Φ S  optimally towards the reference torque Γ ref  and the reference flux Φ Sref  and to command the multi-state switches accordingly, the machine being fitted with a servo-control system implementing the method according to claim  1 .